The carbohydrate modification O-GlcNAc is nearly as abundant as protein phosphorylation in proteins, competes with it, and has extensive crosstalk to regulate signaling, transcription, and the functions of oncogenes and tumor suppressors. However, analysis of protein O-GlcNAcylation currently requires difficult and time-consuming methods such as sophisticated mass spectrometry. There is a need to develop new reagents and simpler methods to study the function of carbohydrate modifications (O-linked and N-linked) of proteins in cancer biology.[unreadable] Even in labs with the ability to make glycosylation-specific antibodies, it is simply too time-consuming and expensive to do that on a scale which would have an impact on the field. DNA aptamers, on the other hand, are readily synthesized and at least 10 times less expensive than antibodies. This project utilizes a new tool, [unreadable]parallel selection of DNA aptamers[unreadable] to rapidly identify high-affinity ligands to tens or even hundreds of glycoprotein or modified polypeptide targets simultaneously. In this NIH Phase I SBIR project, we will demonstrate the utility of our tool for selecting aptamers to numerous important glycoproteins implicated in cancer biology. We will also develop high affinity reagents to specific glycopeptides which are likely to find enormous utility in the understanding of cancer glycobiology.